One mechanism of immunological defense is phagocytosis, in which macrophage cells ingest and destroy pathogenic microorganisms. In receptor-mediated phagocytosis, antibody receptors on a macrophage cell surface recognize antibodies bound to a foreign target and signal the macrophage to begin ingestion. Proposed is an investigation of the molecular events that occur in the initial region of contact between a macrophage and a potential target that lead to the onset of ingestion. In the research, the surfaces of pathogenic targets will be modeled by substrate-supported planar membranes containing hapten- conjugated phospholipids, and the interactions of hapten-specific antibodies with the films will be characterized for different film and antibody properties. The molecular requirements for and effects of the antibody-mediated interaction of macrophage cells with the planar membranes will then be examined. In a complementary approach, macrophage cell surfaces will be modeled by substrate-supported planar membranes constructed either from isolated natural membrane fragments or from purified and reconstituted macrophage antibody receptors and the interaction of antibodies with these model membranes will be characterized. The requirements for and effects of the antibody-mediated interaction of haptenated targets with the planar membranes containing antibody receptors will then be determined. Molecular transport and interaction will be measured with techniques in fluorescence microscopy. High order fluorescence correlation spectroscopy is a new technique that will monitor the formation of molecular clusters. Total internal reflection fluorescence microscopy, which was recently developed specifically for surface phenomena, will measure the equilibrium and kinetic parameters of molecule-membrane adhesion and will monitor molecular orientation. Fluorescence photobleaching recovery will measure lateral and rotational mobility. This research will contribute to the present understanding of (1) molecular events in the macrophage-target contact region during the onset of receptor-mediated phagocytosis, (2) factors that affect protein lateral and rotational mobility in or on membranes, and (3) the physicochemical basis of cell-surface receptor clustering. Development and refinement of techniques in protein reconstitution and surface fluorescence microscopy will be applicable to membrane biophysics in general.